As disclosed in Japanese Patent No. 3690228, ISO-FIX is known as a method for fixing a child seat on a vehicle seat. In the ISO-FIX method, a pair of connectors is provided to the child seat, and a pair of fixtures is provided to the vehicle seat. For example, the pair of fixtures is disposed between a seat cushion and a seat back. A space in a seat-width direction between the pair of fixtures is defined by ISO (International Organization for Standardization).
Each of the pair of fixtures disclosed in Japanese Patent No. 3690228 includes an engaging portion engageable with the connectors of the child seat and a pair of leg portions provided at both ends of the engaging portion. Each of the pair of fixtures has substantially a U-shape as a whole. A rod-shaped member extending in the seat-width direction is provided below the seat back, and the pair of leg portions are welded to the rod-shaped member. A center position in the seat-width direction between the parts of the pair of leg portions which are welded to the rod-like member coincides with the center position in the seat-width direction of the engaging portion.
As described above, the space in the seat-width direction between the pair of fixtures is defined by ISO. Since the fixture disclosed in Japanese Patent No. 3690228 has a configuration in which the above-described center positions are coincident with each other, a layout restriction to be considered between the fixture and the frame or the like provided around the fixture is large. Therefore, for example, even if it is attempted to change the designed space between left and right side frames in the seat frame, it is difficult to respond flexibly to such a design change when the fixture disclosed in Japanese Patent No. 3690228 is adopted.